ADVANCED HIGH-STRENGTH STEEL FRONT RAIL SYSTEM PHASE II

Transcription

1 ADVANCED HIGH-STRENGTH STEEL FRONT RAIL SYSTEM PHASE II John Catterall General Motors Corporation

2 Background Lightweighting initiatives have demonstrated that advanced high strength steels (AHSS) can be effectively utilized for: Mass avoidance strategies Providing required performance Lower overall cost Constraints in implementing AHSS scenarios are: High volume manufacture and assembly Joining and forming

3 Objectives Accelerate the introduction of the higher grades of AHSS (DP800 and above) into vehicles, at little or no cost, and consequently accelerate efforts in vehicular light weighting. Benchmark, develop and document AHSS (DP800 and above) solutions that will balance the interaction of material, manufacturing and performance.

4 Approach Front rail and bumper assemblies from a donated mid-size 5-passenger 4 door vehicle were selected for mass reduction. The vehicle package was configured to accept a transverse - V6 front wheel drive powertrain with a 6 speed transmission. An optional 4 cylinder engine mount was removed from the LH rail and clearances to the worst case package set to 10 mm.

5 Approach An important component to the success of this project was the engineering process that was applied: A stable working envelop was established from day one along with performance targets. The bumper and rail assemblies were designed and optimized as a full system. Design of Experiments (DOE) techniques were used during the optimization phase (incl. non-linear simulations). Designs comprehended manufacturing requirements.

6 Design performance targets were set to, meet or exceed that of the baseline design for: 35 MPH frontal NCAP IIHS frontal offset Static and dynamic stiffness Mass reduction of at least 20% Approach

7 Baseline Bumper and Rail Assemblies Rail Control 2 T = 1.5 mm,hsla340 Trans-Extension T = 2.0 mm, Bake Hardenable 210 Rail Inner T = 1.65 mm, Bake Hardenable 210 Control Reinforcement 2 T = 2.25 mm, HSLA340 Under Body Rail T = 0.95 mm, HSLA340 Control Reinforcement 3 T = 1.45 mm, Bake Hardenable 270 Control Reinforcement 1 T = 1.2 mm, Bake Hardenable 270 Rail Outer T = 1.5 mm, Bake Hardenable 300 Rail Control 1 (Rail extension) T = 2.0 (1.95 & 1.2 mm tailor welded blank), Bake Hardenable 180 & Bake Hardenable 300

8 New Bumper and Rail Assemblies Bumper Beam DP mm Inner Front Rail DP mm/1.2mm/1.4mm Inner Rail Reinforcement DP mm Outer Front Rail DP mm/1.2mm/1.4mm Rail Extension Reinforcement DP mm Rail Extension DP mm/1.2mm

9 New Design Features Symmetric LH/RH rail assemblies. Octagonal 3-piece tailor-welded inner and outer parts: Symmetric flanges Tapered front section Inner rail reinforcement Two-piece tailor-welded rail extension with reinforcement.

10 New Design Attached Components Front Skirt Panel Rear Skirt Panel Bumper Attachment Plate Front Cradle Mountings - Tie Bar Extension Torque Box - Battery Mounting - Rear Cradle Mountings

11 Mass Comparison Results from Computer-Aided Optimization CAO Performed Using Response Surfaces Obtained from DOE Studies Part Baseline Design Mass (kg) New Design LH Rail Assembly RH Rail Assembly Bumper Assembly Total % Mass Reduction

12 Crash Performance Comparison Design Crash Responses B-Pillar Pulse NCAP Peak Decelerations Baseline Design New Design LH RH ms ms ms ms Location IIHS Peak Intrusions (cm) Baseline Design New Design Left Toepan Center Toepan Right Toepan A-B Pillar Closure Crash Targets Satisfied

13 Stiffness Performance Comparison Design Stiffness Responses Static Stiffness Bending Stiffness (N/mm) Torsional Stiffness (Nm/deg) Baseline Design Final Design Static Stiffness First Torsional Mode First Bending Mode Frequency (Hz) Baseline Design Final Design Stiffness Targets Satisfied

14 NCAP RH B-Pillar Pulse Comparison (FEA) 40 B Pillar X-Acceleration (g) Baseline Design Final Optimized Design Time (s)

15 35MPH NCAP Bottom View

16 Comparison (FEA) IIHS RH B-Pillar Pulse 40 B Pillar X-Acceleration (g) Baseline Design Final Optimized Design Time (s)

17 IIHS Frontal Bottom View

18 NCAP Test B-Pillar Pulse Comparison - RH Final Design RH Baseline Design RH acc (g) time (sec)

19 35MPH NCAP Side View Before After

20 35MPH NCAP Bottom View Before

21 Post Crash Observations Good progressive failure of bumper and rail assemblies. No significant deformation of the passenger compartment. All four doors opened after test. No interfacial failures of spot welds.

22 Manufacturing Feasibility of New Design

23 Manufacturing Feasibility Forming simulations performed on all components during design development. Part form tools constructed and run to simulate production intent as close as possible. Laser tailor-welded blanks manufactured. Spot welding schedules established before assembly. Correct gauge and grade of steel were sourced.

24 Rail Extension FEA Simulation FLD Diagram Thinning Diagram Thinning < 15 % Design Feasible with Minor Radii Adjustments

25 Original Prototyping Process Rail Extension Part Name Rail Extension Processes Rough Oversize Profile Flat Blank Single 3 Piece Draw Die Pierce Construction Holes Laser Trim Finish A 3 Piece Single Operation Was Chosen Because of Experience in Building a Similar Part Previously With High Strength Material.

26 Blank Size Rail Extension

27 Rail Extension First Form Single Three Piece Draw Die Made from Kirksite Punch Die Cavity Binder Pad

28 Rail Extension Re-Strike Tool Addition of a Re-strike Finish Form Tool to Finish Forming Side Walls

29 Checking Fixture Rail Extension Inspection Fixture to Verify the Part Surfaces.

30 Final Parts Rail Extension

31 Final Prototyping Process Rail Extension Part Name Rail Extension Rough Oversize Profile Flat Blank Single 3 Piece Draw Die Restrike Operation using Second Form Die Laser Trim Finish Processes Pierce Construction Holes

32 Rail Extension Recommended Production Process Part Name Rail Extension Processes Oversized Flat Developed Blank First Draw Form Second Form Pierce and Trim Outside Profile Final Form Operation

33 Assembly of New Design into Crash Test Vehicle

34 Weld Schedules

35 Assembly Fixture to Weld and Assemble the Rails

36 Assembly Weld Connection Between Front Rail and Rail Extension Weld Connection Between Rail Extension and Floor Weld Connection Between Front Cradle Bracket and Rail Extension Custom Parts Fabricated: Welded and Glued as in the Original Vehicle

37 Lessons Learned

38 Lessons Learned There are no major barriers to executing the new design. An optimal design does not necessarily use all of the available envelop. It is more important to maintain a straight section centroid than it is to have a constant section. Opening up some of the package constraints could have resulted in greater mass savings (rail assembly still has internal reinforcement).

39 LH Design Envelope

40 Load path fit through available envelop Approach

41 Conclusions Design and fabrication of bumper and rail assemblies using AHSS (DP800 and DP980). 23 % mass reduction. Design performance validated by physical test. No major barriers to application.

42 Communication Plan GDIS is official launch of study results. Exhibit Located in exhibit hall. We plan to take the exhibit and presentation to Ford, General Motors, DaimlerChrysler, AISI Steel Companies and the Department of Energy. Please contact an A/SP representative to request more information or to schedule a visit at your location.

43 Thank You!